USDA Hardiness Zone 7a
Frost Dates for 42171 — Smiths Grove, Kentucky
NOAA 1991–2020 normals from Mammoth Cave, KY (760 ft), 6 miles north.
Updated
In Smiths Grove, the last spring frost (32°F) is around April 9 in half of years and has passed by April 29 in nine years out of ten. The first fall frost comes around October 30, as early as October 17 one year in ten, leaving a typical freeze-free season of 204 days (NOAA, Mammoth Cave, KY).
- Last spring frost
- April 9
- First fall frost
- October 30
- Growing season
- 204 days
- Hardiness zone
- 7a
50% probability
50% probability
freeze-free, 50%
0 to 5°F (-17.8 to -15.0°C) coldest night
- First snow
- Rare
- Last snow
- Rare
- Winters with snow
- 44%
- Snow per year
- 4"
median, 1991–2020
median, 1991–2020
8 of 18 observed
NOAA normal
Frost risk by date in Smiths Grove
Half of springs at Mammoth Cave, KY see their last 32°F night by April 9; only one in ten is past it by March 21, and one in ten still has one after April 29. Planting tender crops after April 17 leaves a 30% risk of a frost on them, after April 22 20%, and after April 29 10%. The 20 days between the even-odds date and the one-in-ten date is wider than at 88% of the 113 Kentucky stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 30 in half of years, as early as October 17 one year in ten, and holds off past November 12 one year in ten. A hard freeze of 28°F follows 9 days later, around November 8; in spring the one-in-ten date for 28°F is April 12, 17 days before the 32°F one. The freeze-free season lasts 204 days in a typical year, longer than at 72% of the 113 Kentucky stations; it reaches 227 days one year in ten and falls short of 179 one year in ten. On average 78 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 13 days longer, to about April 22, and return around October 20. Severe cold of 16°F or below comes every winter, usually between December 17 and February 17.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 6 | Apr 11 | Apr 15 | Apr 19 | Apr 22 | Apr 26 | Apr 30 | May 3 | May 9 |
| 32°F | Mar 21 | Mar 29 | Apr 1 | Apr 5 | Apr 9 | Apr 13 | Apr 17 | Apr 22 | Apr 29 |
| 28°F | Mar 5 | Mar 14 | Mar 18 | Mar 23 | Mar 27 | Mar 30 | Apr 1 | Apr 5 | Apr 12 |
| 24°F | Feb 20 | Feb 27 | Mar 3 | Mar 9 | Mar 13 | Mar 17 | Mar 21 | Mar 26 | Mar 31 |
| 20°F | Feb 5 | Feb 13 | Feb 19 | Feb 24 | Feb 28 | Mar 3 | Mar 9 | Mar 14 | Mar 20 |
| 16°F | Jan 20 | Jan 31 | Feb 6 | Feb 12 | Feb 17 | Feb 23 | Feb 27 | Mar 3 | Mar 12 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 6 | Oct 11 | Oct 15 | Oct 17 | Oct 20 | Oct 22 | Oct 24 | Oct 27 | Oct 31 |
| 32°F | Oct 17 | Oct 21 | Oct 25 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 12 |
| 28°F | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 15 | Nov 20 | Nov 26 |
| 24°F | Nov 5 | Nov 8 | Nov 11 | Nov 15 | Nov 20 | Nov 24 | Nov 30 | Dec 4 | Dec 11 |
| 20°F | Nov 12 | Nov 17 | Nov 22 | Nov 29 | Dec 2 | Dec 6 | Dec 11 | Dec 18 | Dec 26 |
| 16°F | Nov 23 | Dec 1 | Dec 6 | Dec 11 | Dec 17 | Dec 23 | Dec 28 | Jan 2 | Jan 11 |
Freeze probabilities 1991–2020 at Mammoth Cave, KY, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 42171 →Compare Smiths Grove with another place →
Weather by month in Smiths Grove
July is the warmest month at Mammoth Cave, KY, averaging 91°F by day and 68°F at night; January is the coldest at 48°F and 29°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 71% of years.
Warmth for growing adds up to 4,960 growing degree days a year (base 50°F), more than at 99% of the 113 Kentucky stations. 39% of them (1,941) have built up by the end of June, and July adds the most, 919. Precipitation totals 53.5 inches a year, most in May (5.2") and least in January (3.7"); May to September bring 42% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 48 | 29 | 3.7 | 100% | 20 | 30 |
| Feb | 53 | 32 | 4.5 | 100% | 16 | 46 |
| Mar | 62 | 40 | 5.0 | 97% | 11 | 149 |
| Apr | 73 | 48 | 4.9 | 71% | 3 | 340 |
| May | 81 | 57 | 5.2 | 8% | <1 | 589 |
| Jun | 88 | 64 | 4.8 | 0% | 0 | 786 |
| Jul | 91 | 68 | 4.9 | 0% | 0 | 919 |
| Aug | 90 | 67 | 3.8 | 0% | 0 | 882 |
| Sep | 85 | 60 | 4.0 | 0% | 0 | 675 |
| Oct | 74 | 49 | 3.8 | 58% | 2 | 371 |
| Nov | 61 | 40 | 4.1 | 99% | 9 | 131 |
| Dec | 51 | 33 | 4.8 | 100% | 17 | 42 |
Monthly normals 1991–2020 at Mammoth Cave, KY (760 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Bowling Green 21 NNE, KY, 14 miles north of Smiths Grove, has a last frost 5 days earlier (April 4), a first frost 1 day later (October 31), a season 5 days longer.
When it snows in Smiths Grove, Kentucky
Measurable snow is rare here: only 8 of 18 winters from 1991 to 2020 recorded 0.1 inch or more at Mammoth Cave, KY, 6 miles away, so there is no typical first-snow date to plan around.
Planting calendar for 42171
| When | What to do |
|---|---|
| January 29 – February 12 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 12 – February 26 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 12 – March 26 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 9 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 7 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 16 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 30 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 42171 is 6 miles from Mammoth Cave, KY, which stands at 760 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 42171 in zone 7a, the band where the coldest night of the year averaged 0 to 5°F (-17.8 to -15.0°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.